Grant: Travel Awards - Institute Community Support

We have developed a noncontact photoacoustic (PA) sensor that uses a low power intensity modulated continuous wave (CW) laser. It can be easily integrated within existing commercial optical microscopes to enable PA imaging of solids and liquids using air as the coupling medium. The PA sensor has two compartments, one is the sample chamber and the other one is a resonator column to amplify the weakly generated PA signal. The PA signal is amplified by means of standing modes in a Helmholtz Resonator. We have developed a multispectral PA system using three wavelengths: 473 nm (Red), 533 nm (blue) and 632.8 (green) nm, each operating at 3-4 mW. The system was used to study (1) methemoglobin and (2) hemoglobin. Methemoglobin is hemoglobin in which the iron in the heme group is in the Fe3+ (ferric) state and therefore cannot bind oxygen. The person with abnormal amount of methemoglobin suffers from disorder called methemoglobinemia. A high level of methemoglobin concentration would also be observed in bleeding. Methemoglobin exhibits relatively high optical absorption at 470 nm and 630 nm compared to normal hemoglobin which has peak absorptions at 420 nm and 570 nm. At the isosbestic point, 530 nm both exhibited almost identical optical absorption. Analyses of blood at single wavelength would not exactly delineate these functional properties. Multispectral studies need to study these functional parameters. Methemoglobin was prepared by treating normal hemoglobin with sodium nitrate (NANO3). The PA studies showed that methemoglobin exhibited relatively high PA signal at 473 nm and 633 nm compared to hemoglobin, and almost same at 533 nm, as expected. The system developed can be used to study the functional properties of these two forms of hemoglobin among other applications.